Display screen or portion thereof with a graphical user interface



1.0 is a front view of a display screen or portion thereof with a graphical user interface in a first embodiment, showing our new design;

Fig. 5.0 is a front view of a display screen or portion thereof with a graphical user interface in a second embodiment, showing our new design; and

Fig. 8.0 is a front view of a display screen or portion thereof with a graphical user interface in a third embodiment, showing our new design.

The outermost broken line rectangle showing the display screen or portion thereof as well as remaining broken lines showing portions of the graphical user interface are included for the purpose of illustrating portions of the article and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 